1. Field of the Invention
This invention relates to a thermal printer for selectively energizing a plurality of heat generators aligned in a thermal head to melt the ink of an ink ribbon and transfer it to a sheet of paper. More particularly, this invention relates to a head position controller for a thermal printer for controlling the contact or separation of a thermal head with or from the paper.
2. Description of the Prior Art
In a thermal printer a carriage moving along a platen is generally provided. A thermal head is mounted on a head mount which is movably connected to the carriage A head pressure contacting lever for thrusting the thermal head against a sheet of paper by pressing the head mount is pivotally secured to the carriage. The head mount is pressed by pressing the head contacting lever with a head pressure contacting plate. The movements of the carriage and the contact or separation of the thermal head with or from the paper are carried out by one electric motor.
In the above-described thermal head, an ink ribbon is fed to the thermal head at a rate equal to the rate of travel of the carriage across the surface of the paper while printing. Printing is produced by contacting the ink ribbon with the thermal head by interposing the ink ribbon and the paper between the thermal head and the platen in order to transfer the ink of the ink ribbon to a predetermined position on the paper.
However, when the ink ribbon is continuously fed in this manner to print on the paper, the ink ribbon must be fed even when there is a gap between printed characters, e.g. a space between words. Further, the ink ribbon, once fed in front of the thermal heads has a number of vacant portions from which the ink has been transferred to the sheet of paper. The previously used portion can not be reused Therefore, the portion of the ink ribbon opposed to a gap in the characters which could be reused is wasted because the printer cannot rewind to use this portion.
Thus, when a large space exists in the printed image information it is advantageous to detect the space, separate the thermal head from the ink ribbon, and stop the feeding of the ink ribbon. This state is called the "tape saving mode".
However, a solenoid is used to contact or separate the thermal head with or from the ink ribbon, thereby switching between the tape saving mode and the printing mode. Thus, the structure of the thermal printer is complicated and expensive to produce.